Photographic color-filter.



R. J. WALLACE & e. GRAMER. PHOTOGRAPHIG COLOR FILTER.

APPLIOAIION FILED NOV.11, 1909.

- 961,42%. 4 Patentd June 14, 1910.

F 17 g; JL ff-l"- of Missouri, and

'certain new and useful TED STATES PATENT mm ROBERT nuns 'wALLAer. ANneus'r'Av examine, or sr. rou'rs mrssoum.

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Patented June 14,1910.

Application filed November 11, 1909. Serial No. 527,368.

To all whom it may concem:

Be it known that we, ROBERT JAMES W41.- LACE, a subject of th King of GreatBritain, residing at the cit of St. Louis and State USTAV CRAM R, a citizen of the United States of America, residing also at St. Louis, Missouri, have invented Photographic Color-Filters, of-which the v overlap of the red and green, while the blue followmg is a full, clear and exact description, reference being ha to the accompany-. ing drawings, forming part of this specifica-- tion.

' It is well known that in the photogra hing of landscapes from nature, the shy,

. owing to its excessive relative brightness (or luminosity) over that of the lan scape and general foreground objects, is always repre sented by too great a density on the photographic negative. This excessive density in the sky portion of the plate results in an abnormal contrast in. the resultant print or positive'from the same, sothat the picture 18 altogether false and untrue with respect to the original view. This error is accentuated apparently when there are cloud forms showing in the sky as they are entirely lost in the reproduction.

- i Our invention is designed to perform two s ecific objects, which, .to be renderedclear, emand a consideration of photographic and opticalfacts; Y

It dis vgellhrknown that vglhite light is coinpose 'o t as rim ues, respective y bluel t, the yellow of. the

red, green and vio solar spectrum being simply, caused by the is formed by the admixture of the green and blue-violet; The brightest hue to the eye is green, while the red comes next in order and then the blue-violet which is very dark. Be-

sides these colors to which the eye .is sensi- ,very truly said to -be does not reprmnt colors with their relativ e tive, there is another region called the ultraviolet which is utterly nvisible.

The ordina ho a bio late may be W P ::olor blindQ and brightness as the eye sees them, but instead almost com iietely reverses the order of brightness. irst: The blue-violet region is represented as being very bright while the invisible ultra-violet is-depicted as. almost equally bright. The green and red are inactive, that is to say,'the plate is not 'sensitive to those hues, hence they arej-represented as practically black; Color in nature Improvements in provement of general photo yet there is stil in density to the of some one 01 more of the primary hues and is visible to the eye either by reflection,

for illustration, green trees and grass, or

by transmission, forillustration, solutions and stained glass. I The ordinary photoor art is simply theresult of the absorption graphic plate or film, therefore, being sensi- .tive only to the blue-violet and ultra-violet,

and insensitive to theother colors, gives,

therefore, a record of the" view or object which is entirely false except for form, and in many instances even the form is falsified .on account of selective color. To overcome this serious defect, various manufacturershave preparedcolor sensitive plates and. films WlllCh are known commercially as iso-l or orthochromatic, panchromatic, etc. These plates are not only sensitive to the ultra-violet and blue-violet, but are also sensitive'to green and red,-respec- 'tively. Althoughthese plates have been rendered sensitive to the green and red, yet it is unfortunately true that their maximum sensitiveness still remains in the'blue-violet ally showing on measurement a difl'erence of 30 to 40 times greater sensitiveness in this region. To reduce this sensitiveness, use is commonly made of a color screen whose function is the dimmin down of the excessive chemical energy 0% the blue-violet and the complete absorption of the ultra-violet.

color filters have been advocated and this purpose, and resulted in the imaphic copies,

ny generally adopted for although their use has overcome; v

It is known-that a photo raph1c plate or and ultrasviolet, the latter two regions actu-- a very consi erableerror to 7 film 'is acted upon by the' ight in proporver tion to the amount of unaltered s1 bromid present at that moment onthe plate or. film, and that after development we have a reduction product which is proportional of the vincident beam. This, however, is

-' only true for intensities between certain oint is reached where. reversal occurs. The" atitude of different makes of plates and logarithm of the intensity films varies, some having' an extended scale' and others but a short scale; ordinarily slow plates and films have a short scale; while high speed plates and films have an extended scale. All photographic papers upon which positive prints are made possess a relatively short scale. It will therefore be seen that in a landscape view embracing foreground and sky, there is an extremely extended scale ofwide limits,- extending from the deepest foreground shadows to the excessively high cloud lights, and utilizing the 'full compass of any plate or film.

The plate or film in turn is beyond the com pass of the paper on which it is printed, so that it is advisable to reduce the range of plate or film tones, otherwise, the sky with its variegated cloud forms cannot be printed without the landscape becomin too dark. On the contrary, if the negative e printed from so that the landscape is correctly represented in its relative brightness, then the sky is represented as a blank and inartistic white region, absolutely devoid of cloud hood such as is used upon ordinary photographic cameras, and B is a holder for our ray filter that is adapted to be attached to and supported by said lens hood. The holder B preferably comprises a plate C having side flanges D and a socket member E fitted to the lens hood and held thereto in any suitable manner. The filter holder is provided with an aperture at the location of the socket member E, in order that the rays of light may pass through the holder to the lens of the lens hood, after passing through the ray filter, which is supported in front of the holder plate C- and within the" flaniges D, the means for such support being pre erably spring tongues F that are secured to the flanges D and exert pressure against the ray filter.

l and 3 designate the plates of glass entering into the construction of our ray filter, both of these plates being in that nature of what is commonly known as optical plane glass. The plate 1 is coated evenly over its entire surface on one side with dyed gelatin and this coating, (indicated at 2, Fig. IV), is dried with proper precaution to avoid the settling of dust upon the coat in The dye stuif incorporated in the go atin usedfor coating the plate 1 is of such nature that it is capable of absorbing evenly throughout the extent of the plate a definite amount of the more actinic rays of the spectrum, with the object in view of re ducing their photographic action. The dye used is preferably a combination of tetrazin and es'culin combined in proper proportions to duplicate the curve of visual luminosity when used with the proper type of photographic plate, or film, although any other suitable dye stuff may be made use of, provided that the dye stufi' possesses an absorption 'in the region of shorter wave lengths than five thousand depending upon the type of photographic plate or film used.

The holder B of our filter, which corresponds in size to the size of the plate 1, has applied to it a coatin 4 which, when first applied to the plate, is plain undyed gelatin. After this undyed gelatin coating has been applied to the plate 3, said plate is laid aside as a proper precaution to prevent ac cumulation of foreign matter upon .its coating, and the coating is permitted to become set. After the coating has become set, the plate is immersed for about one-half 0%) of its length in a dye bath, in order that the portion of the coating entering into the bath may become dyed, after which the plate is removed from the dye bath to permit the immersed portion of the plate and coating thereon to become dried. The dyestuif used in dyeing a portion of the coating on the plate 3 maybe in the nature of a neutral gray, or of any other color possessing an absorption correspondin to the active 1 0 region of the plate, a region that will vary with the sensitiveness Ofdifi'erent types-of plates and films. The line to which the dyed portion of the coating 4:. upon the plate 3 extends from one end of the plate 18 indi- 5' cated at 5, Figs. II, IV, and V, and the surface-that it covers is denoted in Figs. II and V by the heavier shading in these views. After two of the plates 1 and 2 have been coated, the former with dyed gelatin extending throughout its surface to afford an absorblng element for the actinic raysof the spectrum, and the-plate 3 has been coated and dyed throughout a portion of its length with the object in View of causing its dyed portion to reduce, the luminosity of the rays of light passing through it, the two plates are assembled. In placing 'the plates together, their sides having the coatings 2 and 3 thereon are placed so that they face each other, and the plates are connected by a suitable cement, such for instance as balsam, which may be hardened by a baking oper-' ation. I

In our invention the light is filtered through an even coatin of color 2 on the plate 1, and the color in thispoating acts equally u on all of the rays from every point in t e View. and obtains full color correction according to the color sensitiveness tive, and the consequent forcing names of the plate, while the excessive luminosity of the sky sutfers absorption by. passing through the deeper even tint in the coating 4 on the upper half of the plate 3. 5 In the event of the sky line forming an angle by the disposition of foliage, buildtical principles, this line being within focus, it is diffused upon the plate. 4

This color filter may be held position in front of the camera lens "by the holder which fits over the lens hood and. which holder will be capable of' being moved in circular am so that the filter maybe placed at any angle desired with respect to the plane of the lens surface, thus allowing of the dividing shade line of the filter being oriented with the general position or angle of the sky line, (see Fig. V). The filter is i held by suitablemcans, such as the springs F, at any vertical position to which it may be set, that is either hi heror lower with res ect to the center of t e lens. 7 I

- point of real value'in our invention is the fact that {the ray filter may. be slid vertically in its holder so that the upper shaded port-ion of the filter is free of the lens aperture, thus leaving said aperture covered only by the'lower uniformly colored portion of the filter involving the coating 2 on the plate 1, which lower colored portion. consti- 4 tutes a perfectly corrected light filter for use under condltions which do not present abnormally lighted areas, such asjwoodland views, interiors-and portraits, etc. I

. It-will be understood that our ray filter is f;or use only where isochromatic or orthochromatic photographic lates or films are used, and the action of t is filter u on the light reflected from the view or object is threefold:

A. The reduction of the excessive action in the blue-violet and ultraviolet 'towhic h all photographic plates are stron ly sensithelight action of longer wave lengths, dependent "upon thetype of plate used, thus giving correct, (or a proximatelycorrect), color val- ,ues' dependi of the plate utilized; and

' B.; The-.dim min down of the excessive o luminosity orbrig tness of the sky or other bright areaso that its chemical action'up'on the plate is reduced and thus rendering the obtention of detail in those bright re 'ons which would otherwise print white in 5 positive copies made from c negative, and

. but of lesser area than the former.

ng upon the color sensitiveness l pl ates; one of said pla allowing of remarkably superior results .from both a technical and artistic stand oint.

This-light filter as described is especially designedfor' use in landscape photography in combination with colorsensitive plates, although it will be readily apparent that its use is not confined to this class of work, but extendsto objects or views embracing unequally luminosity areas, such as interior views, etc. C. The use of the filter as a color correcting filter on such subjects as do not present sky or other abnormally luminous areas simply by the displacement of said filter 31} vertically along its holder and thus exposing only an equally colored region to the light 'transmitted by the lens.

We are aware of Patent No. 562,642,

rant-ed to McDonough, but our invention 35 is in no Way comparable'with it,.for whereas McDonough makes use of a filter in front of the camera lens yet the object attained is that of equalizing the relative color in-' tensity throughout the view by means of movable'sectors, no selective luminosity correction being attempted or claimed. In our invention, we not only correct the relative luminosity by meansof the semi-dyed plate 3,-but also at the same time correct the photographic action of the relative color values by means of plate 1. We are alsoflaware of the fact that previous patents have beengranted for graduated color filters composed of either an optical or material prism of colored glass or gelatin which being of. full density at one end of the filter sufiers reduction gradually as it approaches-the o posite end.' Our invention difi'ers also om' these in that the color correcting m is of even optical density, while the luminosity correcting film is also of even optical density, No graduated color oan correct evenly the relatiye photographic action of color. throughout the view-the principle being obviously wrong. The idea also previously. atented for the use of alternating strips of difierent colors as a correcting-filter isalso erroneous as mi ht be predicated byan average optical know edge.

' We claim 1. A ray filter comprising two transparent plates;'oneof said plates having upon one of its faces a colored coating for the; correct photographic rendering" of color valua by j the absorption ofthe shorter wave lengths of light; and the other plate having upon one of its faces a colored shadin coating of less area than the coating upon the first platesaid plates being arranged with their coated faces opposite each other and held in assemblage. I

2' A ray filter comprisingiltwo transparent e avin'g upon one of its faces a coating of d ed gelatin for the In testimony whereof, We have hereunto 10 correct photographic ren ering of color valaffixed our signatures, this 5th day of Noues by the absorption of the shorter Wave vember, 1909.

lengths of light; and the other plate hav- JAMES WALLACE ing upon one of its faces a colored shading GUSTAV CRAMER.

coating of dyed elatin of less area than the coating upon t e first plate; said plates In; the presence ofbeing arranged with their coated faces op- E. B. LINN, posite each other and held in assemblage; A.. J. MOCAULEY. 

